The present invention relates to a method for producing containers, such as bottles or the like, with film of thermoplastic synthetic material, and to an apparatus for carrying out such method.
Conventional methods for producing bottle-like containers, starting from a film of thermoplastic synthetic material, generally consist in performing, by means of an appropriate mold, the thermal bonding of two mutually facing strips of film so as to form, between the two strips, pouches that are open at a longitudinal edge of the strips of film.
The two strips thus bonded are preheated at the regions occupied by the pouches and are then inserted in a forming mold composed of two half-molds, facing one another on opposite sides with respect to the strips of film and in which there are molding cavities that are mutually spaced so as to match the distance between the pouches, so that each pouch is located in a molding cavity.
Each molding cavity has, at the open side of the pouches, an opening through which a nozzle is inserted; after closing the mold, said nozzle injects a jet of compressed air in the corresponding pouch, inflating it and causing the regions of the film that delimit the pouch to adhere to the walls of the molding cavity, duplicating their shape.
The substance to be packaged is introduced in the containers thus obtained through the side that has remained open, and the container is then sealed by thermal bonding at the open side.
Containers obtained with this method have considerably lower production costs than containers made of plastics obtained by extrusion and blowing, but they have some drawbacks.
The main drawback is the presence of a ridge that protrudes from the contour of the container and is constituted by the heat-bonded region that joins the two strips of film used to produce the container.
The presence of this protruding ridge prevents the container from assuming an upright position and thus prevents its use for all products which, due to display or utilization requirements, are traditionally packaged in bottles, vials, or in any case containers that have an elongated shape and are meant to be kept upright.
The thermal bonding ridge surrounds the entire container and makes complicated to close it after opening, which is achieved by cutting or tearing the film that constitutes the container. In order to obviate this drawback, containers have been produced with the addition of appropriate closure-supporting inserts for the application of screw closures, but the application of these inserts complicates the production process and increases the production costs of the container.
On the other hand, the thermal bonding ridge prevents the possibility of providing, directly during the molding stage, a threaded neck to allow the application of a closure.
The thermal bonding ridge causes other drawbacks, such as for example discomfort in handling the container and difficulty in packaging and in public display.
The thermal bonding ridge, of these conventional containers does not allow to use the method consisting in covering with a shrink-wrap printed tubular part, in order to achieve excellent presentation to simplify the printing of information or data, avoiding direct printing on the containers.
In order to try to solve at least the problem of the upright arrangement of these containers, it has been suggested to provide, on the bottom of the container, an undercut hollow that is obtained by means of a particular shape of the forming mold and contains the thermal bonding ridge. However, this refinement considerably complicates the execution of the forming mold, and it is not adapted to be used on the lateral surface of the container as well indeed because of problems related to the feasibility of the mold.
Due to the above reasons, the use of containers produced by thermal bonding and thermoforming of a thermoplastic synthetic film has so far been limited to the packaging of samples of products for tests, for advertising, or for the packaging of single-dose products.